The disclosure pertains to contact lenses and contact lens design methods.
Vision errors such as myopia, hyperopia, and astigmatism can be corrected with glasses, contact lenses, or surgery. Contact lenses are favored by wearers for a variety of reasons, including cosmetic appearance, decreased fogging, superior peripheral vision, and to avoid the risks associated with surgery. Nevertheless, contact lenses have significant disadvantages. For example, wearing contact lenses for extended time periods can result in dry eyes, requiring the use of eye drops, and resulting in unnaturally rapid blinking. In addition, many types of contact lenses require careful cleaning, disinfecting, and storage. Surgical methods avoid these disadvantages but have other disadvantages, including surgical risks and variability in the magnitude and stability of the vision correction provided by surgery.
Contact lenses have been developed that correct myopia or astigmatism by reshaping the cornea. Because the cornea provides most of the refractive power of the eye, modification of the corneal curvature is generally adequate to correct vision errors. For example, the correction of myopia requires flattening the cornea while the correction of astigmatism requires making the cornea more spherical. The correction of visual errors by reshaping the cornea is generally referred to as orthokeratology. Contact lenses for orthokeratology have been described in, for example, El Hage, U.S. Pat. No. 5,695,509 and Wesley and Kim, International Patent Application WO 98/52090.
Proper fitting of orthokeratological contact lenses is difficult, and patients often must try several sets of lenses to determine a suitable fit. Such iterative lens selection is both expensive and inconvenient. In addition, in some cases, poorly fitting lenses can lead to temporary vision problems such as ghosting or haze, alarming and discouraging patients. According, improved orthokeratological contact lens and designs methods therefore are needed.
Design systems and methods for designing orthokeratologic contact lenses are disclosed. The methods specify positions and shapes of contact lens surfaces with respect to an anterior surface of a cornea, prior to molding by the contact lenses. The location of the anterior surface prior to molding is referred to herein as the unmolded anterior surface.
According to an embodiment, methods of designing a contact lens comprise selecting a base surface to provide correction of a vision error. The base surface is then positioned with respect to the unmolded anterior surface to satisfy at least one of a volume, cross-sectional area, surface area, or arc length constraint. In further embodiments, methods including positioning the base surface with respect to the anterior surface so that volumes defined by an intersection of the base surface with the unmolded anterior surface are substantially equal. In still further embodiments, the volumes include volumes defined by a relief surface and the unmolded anterior surface.
According to other embodiments, methods of designing a contact lens for shaping an anterior surface of a cornea include positioning the base surface with respect to the anterior surface so that surface areas defined by an intersection of the base surface with the unmolded anterior surface are substantially equal.
Additional embodiments disclose contact lens design methods in which cross-sectional areas defined by an intersection of the base surface and the unmolded anterior surface are substantially equal. In alternative embodiments, methods of designing a contact lens for shaping an anterior surface of a cornea include positioning the base surface with respect to the anterior surface so that arc lengths on the base surface and the unmolded anterior surface are substantially equal.
Computer readable media that include computer executable instructions for performing the above methods are provided.
Systems for designing an orthokeratologic contact lens are provided that include a database for storing and retrieving patient data and a user interface for entering and adjusting patient data. In addition, a design component (a portion of a computer program) specifies a contact lens design based upon patient data to satisfy at least one of a volume, cross-sectional area, surface area, or arc length constraint.
User interfaces for programs for designing an orthokeratologic contact lens include patient data fields for entering and displaying patient data and a design constraint field for specifying a design constraint for designing the orthokeratologic contact lens. The design constraints include a volume, surface area, cross-sectional area, arc length, and elevation constraint.
Contact lenses are provided that include a base zone having a base surface selected to mold the anterior surface of the cornea and a control zone having a control surface selected to align the contact lens on the cornea. The contact lenses also include a relief zone that includes a relief surface that fixes the control surface and the base surface relative to the anterior surface. The control surface positions at least one or both of the relief surface and the base surface relative to the unmolded anterior surface to satisfy a constraint selected from the group consisting of an arc length constraint, a surface area constraint, a cross-sectional area constraint, and a volume constraint.
The invention is directed to novel and non-obvious aspects of this disclosure, both individually and in combination as set forth in the claims below.